The invention relates to the field of silicon wafer processing. Specifically, the invention relates to a system for identifying and tracking the contents of a wafer carrier in a wafer manufacturing facility.
During the manufacture of semiconductor chips, it is necessary to subject a silicon wafer to a variety of processing steps. Processing steps can include, for instance, vapor deposition, heat treatment, photolithography, and cleaning. Each processing step occurs in an enclosed chamber and the wafer must be transported between chambers for subsequent processing steps. During transportation between chambers, the wafer must be kept perfectly clean. For this reason, chip manufacturing occurs in tightly controlled clean rooms in which dust and other contaminants are kept to a minimum. However, even within a clean room environment, the wafers are typically placed in a wafer carrier for protection while they are transported between processing chambers.
In a typical chip manufacturing line, wafer carriers filled with silicon wafers are moved from chamber to chamber on carts. Because some processes take longer than others, it is often necessary for a wafer carrier or a cart full of wafer carriers to enter a queue and wait for a processing chamber to become empty before the wafers are placed in the chamber for treatment. Human operators move the carts full of wafer carriers from location to location and they must keep track of which treatment processes are appropriate for each wafer carrier. Because different wafers can require various processing steps, the operators must keep close track of which processes are appropriate for a given wafer carrier full of wafers. Silicon wafers are relatively expensive and an error by a human operator can cause a significant loss.
In the past, chip manufacturers have tracked wafer carriers by placing bar codes on them. Human operators carry scanners that read the bar codes and instruct the operators regarding the appropriate processes for the wafers. This technique has the disadvantage that bar codes contain read-only information and can not be changed. The bar code is only used as an identifier and it is never updated. Any update of information regarding the wafer carrier must occur within a database connected to the operator""s bar code reader. It would be desirable to have read-write capability for each wafer carrier""s identification tag rather than using read-only bar codes.
Some chip manufacturers have begun to use personal data appliances (PDAs) such as a Palm Pilot(trademark) to store information about the wafers in a wafer carrier. Information in a PDA can be updated and modified as needed to reflect the status of the wafer processing operations. The disadvantages with using a PDA as an identification device are that the PDAs have batteries that must be changed regularly or data can be lost. Also, PDAs are not waterproof and must be removed from the wafer carrier during washing.
The present invention provides a read-write identification tool for tracking the status of semiconductor wafers in a wafer carrier. The identification device is rugged and waterproof so that it can be washed together with a wafer carrier. Information stored in the identification device can be updated as necessary as the wafer carrier moves between processing chambers. Information about the wafer carrier can be read and written from a distance without physically contacting the identification device.
An identification card is attached to each wafer carrier to store and transmit information about the contents of the wafer carrier. The identification card contains a small integrated circuit (IC) chip and a small antenna. The antenna is used to send and receive data and power for the chip is supplied by transmission through the antenna. The identification card is approximately the size and shape of a standard credit card and it is hermetically sealed so that it is rugged and waterproof. The technology used for the identification card is similar to that used for xe2x80x9csmart moneyxe2x80x9d in which a plastic card contains an IC chip and an antenna to store and transmit data about the monetary value of the card.
A reader is supplied to work with the identification cards. The reader includes an antenna that can transmit data to and from the identification card and transmit power to the identification card. Because power is transmitted through the antenna, the identification card does not require a battery and can be made to be very compact.
The reader is in the shape of a wand that an operator can hold in his hand and point at the identification cards on various wafer carriers. Each time the wand is pointed at an identification card, data about the contents of the wafer carrier are transmitted back and forth. The wand contains database information about selected wafer carriers. Data is transmitted to the reader wand from a central database in a host computer via a network connection. The reader wand is connected to the network with a connection adapter that the wand can be placed into.
Based on the database information stored in the reader wand, the operator would be able to quickly determine the contents and status of the wafer carrier. The database information could inform the operator about the processing steps that remain to be completed for the wafers in the wafer carrier.
One aspect of the invention is that the reader wand can be used as a xe2x80x9csniffer.xe2x80x9d In this mode, identifying information about a specific wafer carrier is loaded into the reader wand and the reader wand can then be used to identify a particular wafer carrier of wafers from within a group of wafer carriers. On occasion, a group of wafer carriers may stack up in a waiting area. Each of the wafer carriers may contain different types of wafers and require different processing steps. To find a particular wafer carrier from the group can be difficult and time-consuming. However, the reader wand can be placed into sniffer mode and passed in front of each wafer carrier and to provide a visual or audible notification when it is passed in front of the desired wafer carrier. In this way, a human operator can identify a desired wafer carrier very quickly from a group of wafer carriers.
Another aspect of the invention is that a reader/writer unit is located at each processing station. The reader/writer reads information about each wafer carrier from the identification card on the wafer carrier as it enters the processing station. The reader/writer communicates with the manufacturing control system that operates the processing tool and associated material handling equipment. Based on information provided by the reader/writer, the wafers in the wafer carrier are either rejected or they are accepted and subjected to the process that is being performed in the processing station. After the wafers are processed, the reader/writer updates the identification card to indicate that the wafers have completed that step of processing. This prevents a batch of wafers from receiving incorrect processing steps and allows information about their progress in the manufacturing line to be stored locally in the identification card as well as centrally in the host computer""s database.